A company having a demand contract with a power company performs demand management so as not to exceed maximum demand power (a demand value). The demand contract is a contract in which an upper limit of a power consumption amount for each period, which is called a demand time limit, is defined as the maximum demand power. In order to reduce a power consumption amount (an integrated value) in the demand time limit (for example, for 30 minutes) so as not to exceed the maximum demand power, an electrical facility needs to be operated with low power, and as a technique for that, there is an technique called an intermittent shut-off operation or rotation operation (hereinafter, collectively referred to as an “intermittent shut-off operation”) of an air-conditioning indoor unit. The intermittent shut-off operation is an air-conditioning control method in which power consumption amount is to be reduced by suspending in order a plurality of indoor units for a certain period of time instead of continuously operating them, that is, by performing a so-called thinning operation.
For example, Patent Literature 1 proposes a technique in which a power consumption amount for an initial period in a demand time limit is calculated while external factors, such as an outside air temperature and a solar radiation amount measured N hours before the demand time limit are taken into consideration, the power consumption amount for the remaining time in the same demand time limit is predicted from the calculated power consumption amount, then, when it is predicted that the power consumption in the demand time limit exceeds the maximum demand power, a power amount to be reduced is calculated, and a shut-off time of an electric device is calculated based on the calculated power amount which is a reduction target.